1. Field of the Invention
The invention relates to a process for the production of moldings from cork particles, where the cork particles are bonded with thermoplastic polymers.
2. Description of the Related Art
Production of cork stoppers for bottle cork production produces considerable annual amounts of waste cork. These are ground to give cork granules (cork flour) (transfer cork) and serve as an underlying raw material for the production of moldings from cork particles. To this end, the cork particles are mixed with synthetic polymers and then compressed to give moldings.
DE 1 620 777 A discloses that cork moldings can be produced from cork granules and polyurethane. A disadvantage with the use of polyurethane as binder for granular cork is that the moldings thus obtained cannot then be further processed thermoplastically.
DE 196 29 017 likewise relates to the binding of cork particles with polyurethane, but it also describes the use of thermoplastic polymers as binder. The usual thermoplastic binders in cork processing are ethylene vinyl acetate copolymers, polyvinyl chloride and thermoplastic elastomers (TPEs). Thermoplastic polymers permit the thermoplastic processing of cork particles by means of extrusion or calendering. However, a disadvantage is the high proportion of thermoplastic which has to be used in order to obtain the required mechanical strength, mostly from 50 to 70% by weight, based on the total weight of the molding. A further disadvantage is that the high proportion of polymer prevents the moldings from having the appearance of natural cork.
DE 199 49 593 A1 essentially relates to polymeric binders based on a polymer A1 insoluble in water, and on a water-soluble polymer A2, which is composed of from 50 to 100% by weight of ethylenically unsaturated mono- or dicarboxylic acids, where an amine having hydroxy groups functions as crosslinking agent, and the amine is present separately or is present copolymerized in the water-soluble polymer in the form of an ester of an unsaturated carboxylic acid. Heat-curable polymeric binders are involved here, and these bring about the crosslinking of the components of the binders and of the substrate materials, e.g. cork chips, to give the corresponding, hardened moldings. This application does not disclose how moldings with high mechanical strength can be obtained when the binders used comprise thermoplastic polymers which are not hardened during the production of the moldings.